The disclosure of Japanese Patent Application No. 2002-18620 filed on Jan. 28, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
This invention generally relates to a control system of an internal combustion engine, and more particularly to a control system of an internal combustion engine that is provided with a variable valve train in which the opening and closing characteristics of at least one of the intake valve and the exhaust valve can be changed.
2. Description of Related Art
A variable valve train has been known in the field of internal combustion engines which open and close at least one of the intake valve and the exhaust valve. This variable valve train enables a higher degree of freedom to be ensured with respect to control of the intake and exhaust, which enables the output characteristics and fuel consumption characteristics of the internal combustion engine to be improved compared to when the opening and closing characteristics of the intake and exhaust valves are fixed.
Japanese Patent Application 2001-81435, which is currently being submitted for application by the applicant of this application, for example, proposes an internal combustion engine that realizes a variable valve train function using electromagnetically driven valves. The intake and exhaust valves are electromagnetically driven and enables the opening and closing characteristics of those valves to be changed with an even higher degree of freedom than when a mechanical variable valve train is used. Therefore, this invention proposes a method for controlling the volume of air drawn into the internal combustion engine by controlling the opening and closing timing of the electromagnetically driven valves, and as a result, controlling the output torque of the internal combustion engine.
In the internal combustion engine provided with the variable valve train, the output torque can be quickly changed by changing the opening and closing timing of at least one of the intake valve and the exhaust valve. Therefore, when there is a decrease in idle speed of the internal combustion engine, the output torque can be immediately increased by appropriately changing the opening and closing timing of the valves, so as to prevent the engine from stalling. Accordingly, the variable valve train is an effective mechanism for preventing engine stall while idling.
However, depending on the opening and closing timing of at least one of the intake valve and the exhaust valve, the intake air volume only changes quickly when the intake line pressure is not very low. In other words, when there is a large intake load in the intake line, the output of the internal combustion engine is unable to change much even if the opening and closing timing of at least one of the intake valve and the exhaust valve is changed. Therefore, with the internal combustion engine disclosed in the aforementioned patent application, when the idle speed decreases temporarily, it is possible that, even if the opening and closing timing of the electromagnetically driven valves were changed to compensate for that decrease, engine stall may not be prevented if the intake line pressure were sufficiently low.
In order to solve the foregoing problem, it is an object of this invention to provided a control system of an internal combustion engine that can appropriately return an engine speed to a desired speed, when the engine speed has decreased from that desired speed, regardless of intake line pressure.
In order to achieve the foregoing object, a control system of an internal combustion engine according to a first aspect of the invention is provided with a variable valve train that can change opening and closing characteristics of at least one of an intake valve and an exhaust valve, an intake control mechanism that controls an intake air volume flowing through an intake passage, and a controller. The controller controls the variable valve train so as to increase a torque of the internal combustion engine when the engine speed falls below a desired speed, and controls the intake control mechanism so as to increase the intake air volume when the engine speed falls below the desired speed while the intake line pressure is equal to, or less than, a predetermined pressure.